Apparatus for treating metal



Nov. 3, 1936. A. R. STARGARDTER '2,059,976

v APPARATUS FOR TREATING METAL Original Filecjl'Sept. 4, 1931 3 Sheets-Sheet 1 INVENTOR. .Sagwzdter "ATTORNEY.

IlfllllllPllllll Nov. 3, 1936.

A. R. STARGARDTER APPARATU FOR TREATING METAL Original Filed Sept. 4, 1931- 3 Sl'leets-Sheet 2 INVENTOR. .Acmga/cdec BY Q- (3a-4m ATTORNEY.

Nov. 3, 1936. A. R. s'rARGARDTx-:R v2,059,975

APPARATUS FOR TREATING METAL loriginal Filed sept. 4, 1931 s sheets-sheet 3 nwmvToR. A .ltgazdte/c BY Y' Y ATTORNEY.

Patented Nov. 3, 1936 untreu STATES PA'rsNr OFFICE,

2,059,916 l ArPARA'rUs Fon rREA'rING METAL Albert R. stargardter, Boston, Mass., assigner to' Gillette Safety Razor Company, Boston, Mass., a corporation of Delaware y `Original application September 4, 1931 Serial No..

561,183. Divided and this application April 16, 1932, Serial No. 605,639

22 Claims.

This application isa division of my applicationl Serial No. 561,183, filed September 4, 1931, new Patent No. 2,041,029, dated May 19, 1936, wherein 1 have disclosed and claimed a novel method of controlling the hardening and tempering of a ferrous metal strip.

An object of my invention is to treat continuous lengths of magnetizable metal, Asuch as hardened or annealed steel strips, (or ferrous-` alloys), in such a way as to produce substantial uniformity of a desired character throughout the length of the strip, such as hardness and/or temper, or an annealed condition, in a simple and relatively inexpensive manner.

Another object of my invention is to control the treatment oi a metal strip as it travels in accordance with desired characteristics, such as hard= ness-and/or temper or an annealed condition, of a piece of the same or a similar strip that has been hardened and/or tempered, or annealed, and `which is used as a standard, whereby the strip Seeing treated will have substantially throughout characteristics similar to those of the standard piece and will be substantially free from variations frorn the latter.

Another object of my invention is to cause control of the heat applied to a traveling steel strip by utilizing deiinite characteristics in portions oi the strip, or variations or changes therefrom in the metallurgical characteristics within other portions of the strip itself, whereby to retain a substantially denite or predetermined heat applied to the strip in the heating zone, if required, or to automatically increase or decrease the heat applied to the strip in such zone as may be required, as the strip travels, to cause the resulting product to be substantially uniform throughout its length according to a predetermined standard.

Any change in the microstructure of steel or other ferrous-alloy is accompanied by a change in the electrical or magnetic permeability of the metal. For example, a steel which has been quenched from l600 F. will posses less permeability than if it had been quenched from 15ii F. The same'steel quenched from 1500" F. will posscss less permeability than if it had been quenched from 1460" F., at the same cooling rat-e.

These phenomena are due to the fact that in a given steel or steels identical in composition, microstructure, and prenatal history, the higher the quenching temperature the greater the amount of carbides held in solid solution. The electrical permeability is inversely Aproportional to the amount of carbides ln solidsolution. This principle is also true for annealed steels.

'A steel annealed from 1500 F. at a certain cooling rate will possess greater permeability than the same-steel or steels identical in composition 5 and pre-natal history annealed from 1400 F.,

since the steel annealed from 1500 F. will have less carbide in solid solution than that annealed `from 1400 F.

it also. follows from the above thatln the case of either hardened or annealed steels, (or ferrousalloys) that the electrical permeability is inversely proportional to the cooling rate. Identical steels cooled at the rate of one degree per second will have greater permeability than those cooled at the ratev of 40 per second, etc. Thus Waterquenched steels have less permeability than similar steels oil quenched. y

It is also true that in the case of steels identical in composition and pre-natal history the eleczo trical permeability varies inversely with the net carbon content.

In accordance with my invention, I utilize the electrical permeability of a standard" piece ofv magnetizable metal which has been predetermined as to the desired characteristics to cause the strip to be heat-treated, namely, to be hardened. and/or tempered, or annealed, in substantial correspondence as to desired characteristics in the treated strip of those in the standard strip.

1n carrying out my invention; I provide an electrically heated apparatus through which the strip to be heat-treated is propelled and electrical devices through which the heat-treated strip travels. Said devices are adapted to react to electrical permeability changes or variations in such strip as compared to a standard piece of similar material in said devices to register, indicate and/or control automatically any such changes or variations from the standard piece to cause the heating apparatus to apply a required temperature to a traveling strip, such as maintaining a given heat or reducing such heat for a required period, and for restoring a higher heat as may be required, to cause the strip to be heat-treated so 4:5

that its desired characteristics will, throughout its' length, substantially correspond to those of the standard piece.

1n a particular embodiment of my invention as illustrated in the accompanying drawings, proa 5G vide an electrically heated induction furnace having an automatic control switch in its supply line, means to continuously propel a metal strip through the furnace, means to quench the' heated strip, a pair oi transformers 55 ,(Figs. 3 and 4).

respectively having passage-ways for the strip under treatment and for a piece of standard metal, the secondaries of the transformers having windings electrically opposed, in an electrically balanced circuit including a galvanometer, a mirror operative by the galvanometer, a photo-electric cell to receive a light beam from the mirror, a lens system serving to focus the light emanating from the mirror upon the photo-electric cell window, and a circuit controlled by the photo-electric cell including devices to operate the aforesaid switch. The arrangement described is such that a standard metal piece will be placed in one transformer and the strip after emerging from the quenching and/ or tempering means will travel through the other transformer. If the last named portion of the strip corresponds to the standard piece the light beam fromthe galvanometer mirror will rest upon the photo-electric cell, causing the circuit through the furnace to remain closed for standard operation. Should the furnace temperature rise and change the then existing characteristics of the quenched strip a differential will occur in the circuit of the transformer secondaries causing the galvanometer to operate the mirror to remove the light beam from the photo-electric cell, thereby causing the latter to ceasefunctioning and the circuit through the furnace will be broken. When the furnace drops to an appropriate temperature, (and the characteristics of the quenched strip and the standard piece correspond), the galvanometer circuit will balance and the galvanometer will operate and cause the light beam to again fall on the cell to cause closing of the furnace switch to restore heating of the latter. In this way the temperature of the furnace may be maintained at such a condition as will produce a substantially uniform hardening of the strip throughout its length in substantial correspondence with the standard" piece.

My invention also comprises novel details of improvement that will be more fully hereinafter set forth and then pointed out in the claims.

Reference is to be had to the accompanying drawings, wherein Fig. 1 is a side elevation of an apparatus adapted to carry out my invention;

Fig. 2 is a plan view of the apparatus;

Fig. 3 is a sectional view partially on line), 3 inFig. 2;

Fig. 4 is a cross section on line 4, 4 in Fig. 3;

Fig. 5 is a detail view illustrating the galvanometer and photo-electric cell in operative lrela.- tion;

Figs. 6, '1' and 8 are detail views illustrating various positions of the galvanometer mirror with respect to the photo-electric cell,'and

Fig. 9 is a diagrammatic view of the electrical devices for controlling the furnace temperature.

Similar numerals and letters of reference indlcate corresponding parts in the several views.

Upon a suitable frame I is mounted an electric induction furnace 2 through which a strip A of metal, such as relatively thin steel, is to be propelled in a continuous way. The furnace illustrated comprises a mufiie 3 of suitable metal, shown in tubular form, open at both ends of the passage of strip A. The muille is enclosed in insulation 4 around which is a conductor coil 5 that is enclosed in insulation 8. Said parts are shown enclosed'in an outer protective casing 1, The coil 5 is shown connected with conductors 8 and 9 leading from a high frequency converter I of any desired construction,

to be supplied from an A. C. line source II, I2. The muiile will be heated by induction from the coil for heating the strip A as it travels. The coil 5 is shown in tubular form and connected with rubber hose at 5a, 5b, to be supplied with running water, cold water running through the tubular coil thus keeping the coil cool. Said strip may be supplied on a reel I3 and wound on a take-up reel I4 in a Well known Way. Any suitable propelling means for strip A may be provided. I have illustrated a pair of opposed rolls I5 and I6 suitably journaled for gripping and feeding the strip. The roll I5 is shown provided with a gear I1 in mesh with a worm I8 operative by chain I9 on sprockets 20, 2| driven by a motor 22 to propel the strip A through the furnace at a substantially constant speed of travel. At 23 and 24 are cooling plates between which the heatedlstrip A passes in a quenching zone from the furnace or heater for chilling or quenching the heated strip. A cooling water tank is indicated ai. 25 on'plate 24. The heated strip will be quenched in a well known way by passing between' the chilling plates.

At 26 and 21 are a pair of step-down transformers having primary windings 28 and 29 in series in a circuit, shown including conductors a, b and c, (Figs. 1 and 9). A switch at d permits connection of said conductors .with the A. C. supply line conductors at e. An adjustable resistance is indicated at f for the conductor c, (Fig. 9). The secondary windings 28 and 29' of said transformers are oppositely wound and are thus electrically opposed, their terminals being shown connected by a conductor 30, the other terminals of the secondaries 28' and 29' being respectively connected by conductors 8l and 82 with the movable coil 33 of alternating current galvanometer 34. The said secondaries have no permanent cores and the transformers are so constructed as to be in perfect electrical balance until strip A has passed through an electrical field in secondary 28' Aand a standard metal piece B is placed to rest in an electrical field in secondary 29', serving as cores within the secondaries. The primaries and secondaries have passage way 28" and 29", respectively, to receive the strip A and standard piece B. The circuit through coil 3S of the galvanometer eld circuit is controlled by switch 31 connected with the A. C. supply line 38 to receive suitable electric current, (Fig. 9). A mirror or refiector 4I is connected with movable coil 38 so as to be rotated thereby. At 42 is a light source, such as an electric lamp, shown located within the casing 40, to cast a light beam on the mirror 4I. The lamp 42 is shown enclosed within a shield 43 having an aperture 44 for the light beam. Different angular positions of the mirror, on one side or the other of a pre-determined position, such as in Fig. 7, are utilized to indicate and/or control the flow of current through the coil 5 of the furnace in accordance with difference in characteristics between the standard piece B in transformer 21 and the portion of strip A passing through the transformer 26. The arrangement is such that when the mirror is in the position shown in Fig. 7, the circuit for coil 5 should be closed and if the temperature of the furnace should unduly rise, the strip A will be so heated as to cause a difference in characteristics between the portion of the strip passing through the transformer 26 and the standard piece B to cause unbalancing of the circuit through the secondaries ofthe transformers,

25 position of the mirror iii.

40`the .sv/itch controlled line 45 :rept open by a spring positions of the mirror from the position of the an angular position at one side oi the position of Fig. 7, such as to the position shown in Fig. o, and the circuit for the coil will be broken automatically. When the temperature of the furnace 5 has dropped so that the characteristics of the portion of the strip passing through the transformer 26 compare with the characteristics of the standard piece B, the galvanometer coil 33 will operate to return the mirror to its normal position, such as in Fig. 7, whereupon the circuit through the coil 5 will be closed automatically.

If a still greater divergence in the metallurgical characteristics of the pre-treated strip should exist so that the portion passing through the transformer 2li shows greater permeability than was the case in that portion giving rise to the mirror position in liig. 7, the mirror M will move still farther to the leit, (to position shown in Fig. 8), and the furnace heating circuit-will remain closed until the traveling strip, due to this heating, will regain properties oi the strip causing the mirror position shown in Fig. 6. My invention includes means to automatically control the circuity through the heater coil 5, in accordance with the Devices for such purposes are arranged as follows- At is a photo-electric cell supported by frame i in position to receive the light beam reiiected :from the mirror. The circuit 45 of the photo-electric cell through the amplifying tube power to operate the magnetic contacter have illustrated a transformer whose secondary Winding 5t is included in the circuit ci the' photo-electric cell and z.ff/hose primary winding is supplied with suitable il. current through a grid-leale o, a fixed condenser It and a potentiometer i are shown for the photo-electric cell circuits. A reiay lati, as controlled by a solenoid coil 35 in the circuit 5i of the photo-electric'cell, may' be normally When the light baarn is upon the photo-electric cell, sufficient power from photo-electric cell, amplified through the system shown will energize coil et: to cause the relay lill to close the line through the coil il@ so of the normally open contactos to cause the latter to close the circuit oi line il. i@ to the converter to supply current to coil 5 oi iurnace. contactor being normally held open 'oy a spring or by its own Weight.

In order to assure that the iight beam troni mirror @il will not ail-ect the photo-electric cell llt when the mirror is in certain positions but will affect said cell when the mirror is in other positions, i provide the casing il@ with a iront wail till and with a iront opening till, as indicated in i'figs. 5, 7 and S. When the mirror is in the position shown in Fig. o, the light beams or rays `from the mirror will be obstructed by the viali Alli so @5 as not to affect the cell ilil, and when the mirror has moved a suitable distance, such as to the positions shown in Figs. 7 and 8, the light beam may be cast upon the cell i5 through the opening itil" of the casing titl. In order to assure the concentration of the light beams or rays on the photo-electric cell in all appropriate positions or mirror di, I interpose lenses at 5d and Si between the mirror and the cell to intercept the beam or light rays from the latter and rectify them so that they Will be directed upon the cell in diiierent Tl e coil may be a solenoid coil, the.

latter shown in Fig. 6 to its positions shown in Figs. '7 and 8. The lenses are shown connected together by an interposed tube t2 through which the rays may pass from the mirror. The tube 62 may be supported by casing 40 by means of a post BS, (Fig. 5). The lens Si) is shown having its convex surface opposing the mirror and the lens si has its convex surface opposingthe photoelectric cell, whereby in different angular positions oi. the mirror, with respect to the lenses, the light beam or rays from the mirror will be caused to be directed against the cell, convergin to a point at the cell Window.

The operation may be described as follows: Two pieces of strip metal of similar manufacture to that of the strip A to be treated and bearing the structure desired to be obtained through the treatment of strip A may be placed in the passageways of the transformers 2d and il. The primary coils of the transformers and the galvanonieter held circuit are then closed at .the switches d and 3l to energize the circuits, and resistance f will loe adjusted until the mirror 6i assumes a position to cast the beam upon the photo-electric cell, such as indicated in Fig. 7, for causing closing oi the respective circuits at the relays 5Fl and dil, whereby current will be caused to dow through the coil 5 oi the furnace lor heating the latter. The standard piece B vis allowed to remain in the transformer 2l, the other piece is removed from the transformer 2t and the strip il. to be treated entends .from the furnace and is inserted in the transformer and passed through the rolls iii and l@ to the reel itl. Assuming that the standard piece B has been quenched from 1506" l. and it is desired to have the strip il. heated to 15% as it travelo, the motor @il will be caused to operate to propel strip .fr when the temperature oi the furnace has reached the desired degree, suoli as ioilil" F. So long as the furnace temperature rernains conetant and the strip A is' heated and quenched as it travels to correspond in desired characteristics to those oi? the standard strip B, the circuit of the primary windings il@ and @il and the sucked circuit oi the secondaries o the transformers will remain balanced and the galvanorneter will cause the :mirror to loe in suoli a position as to cast the light beam vthrough the lenses upon 'the photweiectric cell to maintain the relays closed at and ilil to continue the flow oi current through the iurnace coil it such time, the

quenched strip A passing through the secondaryand the standard piece E in secondary Eil correspond in the desired characteristics. Should the traveling strip A, at some portion after quenching, as it passes through said secondary, vary from that of the standard piece, such as to require less heat, a differential will occur in the circuit o the secondaries oi the transformers, because oi different characteristics between the standard" piece and the said portieri ci' the strip, thereby causing operation of the galvanometer to actuate the mirror and move the light beam from the photo-electric cell, as shown in 6. Thereupon the photo-electric cell circuit controlling the coil 55 will cease functioning and the spring 5t will cause the contacter to brealr the circuit 5l whereupon the spring es will operate the contacter it to break the circuit of the line i i, i2 and the current will ne broken from the furnace coil il. The traveling strip A will continue to be heated by the remaining heat in the furnace to bring the strip substantially to the characteristics of the standard piece. When the net temperature of the furnacedrops, say 10 F., and the characteristics of the strip A correspond to the characteristics of the standard piece B, the circuit of the transformers secondaries will again be balanced and the galvanometer will operate the mirror 4I to cause the light ray to fall on the photo-electric cell to cause closing of the contactor 54 at the circuit 51, whereuponv the coil 58 will be energized and cause closing of the contactor 48 of the line circuit II, I2 to restore the current to the furnace coil 5 to continue heating of the latter. The operations described occur successively as variations in characteristics occur in the heated and quenched strip with respect to the characteristics of the standard piece B for required treatment of the strip A as it travels. If the furnace temperature should rise above the proper degree and thereby change the characteristics of the heated and quenched strip A as com-- pared to the standard piece B, the circuit of the secondaries 28' and 29' through the coil 33 of the galvanometer will be so changed as to cause operation of the mirror 4i to remove its light beam from the photo-electric cell, (Fig. 6), thereby de-energizing coil 55 to cause break of circuit 51 to cause consequent breaking of circuit at switch 48 and shutting roil of the current through coil 5 of the furnace until such time as the furnace sufilciently cools to cause the quenched strip A to again correspond with the standard piece B, thereupon the circuit of the secondaries through coil Il will be again balanced and cause theI mirror to cast alight beam on cell 45 to cause closing of circuits at contactors 54 and 48 and to restore current to coil 5. Should the furnace temperature remain absolutely constant, any structural differences inherent in the strip will become apparent and will be automatically compensated for to produce a uniform product. For example, if portions of the hardened strip contain less carbide in solid solution, the hardening temperature applied to portions of strip A richer in dissolved carbide will yield a quenched product higher in permeability when applied to the portion leaner in dissolved'carbide, of the strip A, (e. g., leaner in dissolved carbide in the pre-hardened state) passes through transformer 28 after being quenched at the prevailing temperature, it will possess greater permeability than the strip higher in dissolved carbides, and will cause the galvanometer light beam to be turned to fall on the photo-electric cell, a though the furnace temperature has fallen, or. in other words, as though the pre-hardened strip richer in dissolved carbide had been quenched from a lower temperature. The action of the photo-electric cell with the light beam upon it, will cause the operation of the contactera I4 and 48 to cause current to flow through the furnace coil 5 until that part of the strip-A leaner in dissolved carbides passes through the furnace and upon arrival in the transformer 2B' of the strip richer in dialolv'ed c'arbides in the original state, the permeability of the quenched strip willbe again decreased, and the galvanometer mirror will operate to cause the light beam to pass from the photo-electric cell thereby causing operation of the oontactors N and Il to break their circuits, toshut oi! the current 'flow to coil D, to cause automaticcooling of the furnace, to compensate for the changed character` istics of the strip A being treated. The furnace A so that when such portion temperature will be constantly altered to meet any changes in the continuity of the metallurgical characteristics within the steel strip A as compared to the standard piece B. The resulting product will be substantially uniform since the hardening temperatures will have been controlled so as to produce a substantially uniform amount of carbide in solution in the steel strip A. The automatic temperature changes described may be secured quickly enough to maintain a high degree of uniformity within the strip A which constantly emerges from the hardening system, through use of a high-frequency induc- -tion furnace, which is unusually adaptable to rapid temperature alteration.

While I have described the construction and the operation as applied to hardening and chilling a strip A of steel, it will be understood that my invention may be utilized for tempering hardened steel strips, as well as controlling annealing of ferrous metal strips, and quenching rates of hardened steel, and also for controlling the speed of travel of a strip through amiachine of the character described. In the drawings, I have illustrated means for tempering the hardened and quenched strip as it travels from the furnace described. The furnace 2' having a munie-3' and conductor coil 5' connected withline conductors 8 and 9', similar in construction to that described with respect to the furnace 2, is shown mounted on frame I, beyond Ithe transformer 26, in alignment' with said transformer, whereby the hardened and quenched strip A from furnace 2 will travel through the furnace 2 to be heated to the desired extent for tempering the hardened strip. At a suitable distance from the furnace 2 for cooling the strip A is a transformer 26' for passage of said strip, and at 21' is a transformer to receive a standard? tempered piece B'. A` galvanometer and mirror similar to those previously described is within a casing 40 and conductors 3|' and 32' connect the movable coil of the galvanometer with the transformers 2S and 21 in manner described respecting corresponding parts. A photo-electric cell l5' is in position to receive a light beam from the mirror in casing 40. An ampler 41 and transformer 4l', similar to the amplifier 41 and transformer 49, having the supply lines 5l', and the conductors Ii' and Il' of the photo-electric cell circuit, corresponding to parts previously described, will control the circuit through the conductors l' and I' for the coil 5' in manner previously described, and conductors at 38' supply the g'alvanometer field. Switches and relays '(such as d, 31, I8 and 54) for the corresponding circuits, as previously described, including means, such as solenoids like 58 `and 55 to operate the associate contactors, together with other adjuncts previously set forth. will be supplied to complete the electric devices, whereby a normally balanced opposed circuit between the secondary windings of the transformers 26 and 21 will be established.

A standard piece B', previously hardened and tempered as desired, will be placed in the passageway of the transformer 21' to serve as a core therein, and the hardened and quenched strip will be passed through the mume 3' and through the passageway of the transformer l26', as illustrated in Fig. 1. Suitable high-frequency electric current will be Supplied to the coil I' to cause the munie 3' to be heated by induction to the desired degree.l The operation of the gavanometer and its mirror inassociation with the photo-electric cell 4B', will be similar to that previously described, in connection with the bucked circuit between the secondaries ,of the transformers 26' and 21' for causing control of the flow of currentthrough coil for maintaining the required `temperature of the munie 3',\in accordance with the characteristics of the tempered strip A passing 26' correspond to the characteristics of the standard piece B', the corresponding galvanometer mirror will be in position to maintain a beam on the photo-electric cell d5' to keep the muiiie o' at a desired temperature for standard operation. Should the temperature of the mufile 3 rise and change the then existing characteristics of the adjacent portion of the tempered strip A, a dierential will occur in the circuit of the secondaries of the transformers 26' and 2l', causing the associate galvanorneter to operate its mirror to remove the light beam from said cell, thereby causing the latter to cease functioning and the circuit to the coil 5" will be breiten. The tempering of the strip will continue and when the ternperature of the mume 3' drops appropriately (and vthe characteristics of the tempered strip passing through thetransiormer 2&3' and the standard piece B"correspond), the galvanometer circuit will balance and the galvanometer will operate to cause the light beam to again fall on the cell 45 to cause now of current throughvthe coil o',

to restore heating to the latter. The operations described follow in succession as the tempered strip travels to maintainthe tempering of the strip in substantial accord with the desired characteristics of the tempered piece E".

in accordance with the arrangements set forth,

'a travelingT steel strip may be hardened and quenched, and then tempered, successively in a continuous manner, and the 'iinished tempered strip may be 'wound on the rcel ll in an expeditious and economical way, with the assurance that the hardening and the tempering 'of the -A strip `will be throughout its length in accordance with the standards of hardness and tempering desired to have characteristics of hardness and temper substantially correspond to Vthose oi the standard pieces selected, such as E and B'.

While i have illustrated and described means for hardening and subsequently tempering a continuous strip .oi metal as it travels, it will be understood that astrip may be hardened without at the same time tempering it, or that a strip previously hardened elsewhere may be tempered oy passing through a furnace 2. .an apparatus may be provided with a hardening furnace or heater and its adjuncts as described or with a tempering furnace or heater and its adjuncts described. it also will be understood that a strip may be passed through either of the furnaces or heaters described for armealing the strip in con junction with a standard annealed piece in an appropriate transformer, whereby the circuit through the secundarias of two transformers de scribed will be controlled :for controlling the tempesatura of the annealing furnace or heater in manner described with respect to hardening or tempering a metal strip. The invention also may may be quickly heated to the desiredtemperature and may be maintained approximately at such temperature because the supply current for the furnace may be turned on and on automatically in accordance with the correspondence of desired characteristics'between the standard piece B or B' selected and the portion of the strip being treated, since the current flow will continue so long as the proper heat is applied to the strip in accordance with its electrical permeability or the characteristics utilized. When such permeability or characteristics vary from that of the standard piece in such a manner as to aiect the "desired treatment .of the strip the current iiow will be automatically turned off and on, as required, and the furnace control may thereby be secured automatically, and the temperature of the furnace may be quickly altered to meet any changes in the continuity of. metallurgical characteristics within the steel strip. It is distinguished .from the previous practice of furnace control from an arbitrary, pre-determined temperature maintained by stationary thermo-couples within the furnace. The' resulting product, according to my invention, is substantially uniform since the hardening or the tempering may be so controlled as to constantly product a uniform amount of carbide in solution in a traveling steel strip, whereby to effect the desired results therein. This is effected because the automatic temperature changes derto propel. a strip through the furnace, and'devices to control the new of current through the furnace, said devices including means through which 'the heated strip passesand means to retain a standard piece in said devices, whereby differences in permeability between the portion of. the strip passing through. the second named means and the standard piece will cause operation of the furnace control means.

2. An apparatus for heat-treating a ferrous metal strip comprising an electric furnace, means to cause travel of the strip through the furnace, and control means for the circuit of the furnace, including transformers having their primary circuits in'series and their secondary circuits in normally opposed relation in a circuit, one of said to receive a standard metal piece, said control f :means being operative through a difference' in permeability in the portion of the strip in the first named' 'transformer andthe standard piece for unbalancing the circuit of said seconclaries to cause operation of the said control means to vary the ovv of current for thc'furnace.

3. An apparatus for heat-treating a metal strip comprising an electric furnace, means to cause travel of the strip through the furnace, and means to control the flow of current through the furnace, including a pair of transformers respectively having means to receive said strip'and a standard piece of metal, said, transformers having their primaries in series, the secundarios of the transformers being connected in opposed relation in a circuit, an electrical instrument having a member in said circuit, and means controlled by said instrument to operate the furnace (iii control means to vary the flow of current through the furnace in accordance with different characteristics of permeability between the portion of the strip in its associate transformer and said standard piece.

4. An apparatus for heat-treating a ferrous metal strip comprising an electric furnace, means to cause travel of the strip through the furnace, means to control the flow of current through the furnace, a pair of transformers respectively having means to receive said strip and a standard piece of metal, the transformers having their primaries in series, the secondaries of the transformers being connected in opposed relation in a circuit adapted to indicate variations in permeability in the strip as it passes through one of the transformers, an electrical instrument havling ay movable member included in said circuit,

said instrument having an electric eld, means to energize said ileld, and means controlled by the operation of. said movable member to cause operation 'of the rst named control means to vary the ilow of current through the furnace.

y5. An apparatus for heat-treating a ferrous metal strip comprising an electric furnace, means to cause travel of the strip through the furnace, means to control the flow of current through the furnace, a pair of transformers respectively having means to receive said strip and a standard piece of metal, the transformers having their primaries in series. the secondaries of the transformers being connected in opposed relation in a circuit including a movable coil of a galvanometer, the current insaid circuit being adapted to indicate variationsv in the permeability of the strip passing through one of the transformers, and means controlled. by said movable lcoil to cause operation of the heater control means to vary the flow of current through the furnace.

6. An apparatus for heat-treating a.ferrous metal strip comprising an electric furnace. means to cause travel of the strip through the furnace, means to control the flow of current through the furnace, a pair of transformers respectively having means to receive said strip and a standard piece of metal, the transformers having their primaries in series, the secondaries of the transformers being connected in opposed relation in a normally balanced circuit including a coil of an electrical' instrument having a movable part operative by an unbalanced condition in the circuit through said secondaries and coil, the current in said circuit being adapted to indicate variationsin. the permeability of that portion of the strip passingfthrough one of the transformers, a mirror operative by said movable part, a light source for the mirror, a photo-electric cell and a circuit controlled thereby including means to control the rst named control means for varying the flow of current through the furnace.

7. An apparatus for heat-treating a ferrous metal strip comprising an electric furnace, means to cause travel of the strip through 'the furnace, means to control the flow of current through the furnace, electrically operative means having passageways for the strip and for a standard piece respectively, and means operative by the last named means according to differences in permeability between the portion of the strip and said standard piece in said electrical operative means to' register'variations in said characteristics.

8. An apparatus for heat-treating a ferrous metal strip comprising an electric furnace,

means to cause travel of the strip through the -furnace, means to control the ilow of current through the furnace, similar devices having passageways for the strip and for a standard piece respectively constructed and arranged to generate a current dependent upon the relative permeability of the strip and standard piece and having means to casta light beam, a light source for said beam, a photo-electric cell to receive said beam, and electrically operative means controlled by said photo-electric cell to operate the heater control means to vary vthe flow of current through the furnace.

9. An apparatus for heat-treating a metal strip comprising an electric furnace, means to cause travel of the strip through the furnace, means including a relay to control the flow of current through the furnace, similar devices having passageways for the strip and for a stand' ard piece respectively constructed and arranged to generate a current dependent upon the relative permeability of the strip and standard piece and means to cast a light beam, a light source for said beam, a photo-electric cell to receive said beam, electrically operative devices to ccntrol said relay and a circuit controlled by the photo-electric cell including means to control the operation of said last named devices.

10. An apparatus for heat-treating a ferrous metal strip comprising an electric furnace, means to cause travel of the strip through the furnace, means to control the flow of current through the furnace, similar electrical devices having passageways for the strip and for a standard piece respectively arranged to generate a current dependent in direction upon the relative permeabllity of the strip and the standard piece, and means to cast a light beam, a light source for said beam, a photo-electric cell to receive said beam, a circuit for said celll an amplifier controlled by said circuit, a circuit for the amplifier, a relay having a coil in the amplifier circuit, and means controlled by said relay for controlling the circuit through the furnace.

11. ,An apparatus for lheat-treating a ferrous metal strip comprising an electric furnace, means to cause travel of the strip through the furnace, a relay to control the flow of current through the furnace, electrically operative means having passageways for the strip and for a standard piece respectively and means' to cast alight beam varying in its direction in accordance with differences' in permeability between the strip and the standard piece, a photo-electric cell to receive said beam, a circuit for said cell and electrically operative devices to control said relay, said devices being controlled by the circuit of the photoelectric cell.

12. An apparatus for heat-treating a ferrous metal strip comprising an electric furnace, means to cause travel of the strip through the furnace, a relay to control the flow of current through the furnace, electrical devices connected by a normally balanced circuit andhaving means to receive the traveling strip and a standard piece 'and to compare the relative permeability thereof,

cause travel of the strip through the muiiie, a supply line for the muille including a contactor, and electrically operative devices to control the contactor including devices operative according to diierence in permeability between the portion of the strip heated by passing through the muille and a standard piece of metal for causing operation of the contactor. l

i4. An, apparatus for heat-treating a metal strip comprising an electric furnace including a tubular muilie for the strip and an electric conductor in inductive relation to the munie, means` tdcause travel of the strip through the muille, a supply line for the muiile, and means to control flow of current through the supply line including a pair of transformers to respectively receive said i strip and a standardpiece, said transformers having their primaries in series and their secondaries in opposed relation in a circuit arranged. to indicate differences in the permeability between the standard piece and that particular part of the strip which is passing through on of the tran..- forrners, an electric instrument having a movable coil included in said circuit, means to supply said instrument with current, a contactor to control said supply line, and devices operative by said coil to control said contactor.

15. An apparatus as set forth in claim 14 in which said devices include a mirror operative by said coil, a photo-electric cell to receive a light beam from said mirror, a circuit and devices controlled by the said cell to control said contactor.

16. Apparatus for heat treating a steel object to produce a predetermined value of a selected magnetization affecting property therein corn.- prising a heating device,l an induction device having a primary and secondary winding, means for advancing successively occurring portions of an object in heat exchanging relation to the heating device and then through the eld of said induction device, and means operatively connected to the secondary to vary the heat exchange relation between the heatingvdevice and portions of the object being heated in response tovariations vin function of said selected property occurring in said secondary in respect to portions of the object in the field of said primary.

l'l. Apparatus for heat treating a steel object to produce a predetermined value of a selected magnetization aiecting property therein comprising a heating device, an induction device having a primary and a secondary winding, means for advancing successively occurring portions of an object in heat exchanging relation to the heating device and then through the field of said primary, means for regulating the effective temperature of the heating device and means operatively connected to the secondary and to said temperature regulating means to vary theheat exchange relation between the heating device and portions of the object being heated in response to variations in a function of said selected property occurring in said secondary in respect to portions .of the object in the field of said primary.

18. Apparatus for hardening strip steel, comprising an electrically heated furnace and cooling plates located in alignment for the passage of a strip through them, a transformer having a passageway for the hardened strip to enter as it leaves said cooling plates, a second transformer having a passageway for a standard strip, a circuit for energizing the primary coils oi' both transformers, and means for controlling the flow of current to said furnace in accordance with variations in the response of the secondary coils of said transformers.

19. Apparatus for tempering strip steel, comprising an electrically heated hardening furnace and an electrically heated tempering furnace arranged in 'alignment with cooiing plates located between them and all presenting passageways for a moving strip of steel, principal transformers located at the exit end of said cooling plates and of said tempering furnace and 'having passageways therein, auxiliary standard-holding transformers each. having its secondary coil in circuit with that of one of said principal transformers, a circuit energizing the primary coils of all said transformers, and means for controlling the flow of current to bothoi said furnaces in accordance with variations in the response of the secondary coils of the respective transformers.

20..An apparatus for heat-treating a ferrous metal strip, comprising an electric furnace having a heating circuit, means to propel a strip through the furnace, and circuit-controlling means cornprising a pair'of transformers respectively having a passageway for a` strip which has been heated in the furnace and for a standard piece of meti, said transformers having their primaries in series and having their secondaries in opposed relation in a circuit arranged to indicate differences in permeability between the standard piece and the part of the strip which is passing through one of the transformers, an electrical instrument having a movable coil in said secondary circuit and means in said instrument to energize said coil, a. mirror controlled by said coil, a photo-electric cell arranged to receive a light beam from said mirror, a circuit for said cell, and electrical devices controlled by said circuit for automatically interrupting the said heating circuit of the furnace.

21,. An apparatus for heat-treating a ferrousy metaistrip as set forth in claim 20, in which the electrical devices include an amplier controlled by the circuit of the cell, a circuit for the amplier, and a contactor controlled by the amplier circuit.

22. An apparatus for heat-treating a ferrous metal strip as set forth in claim 20, in which the electrical devices include an amplifying device controlled by the circuit of the photo-electric cell, a circuit. for the amplifying device including a coil, a contactor operated by said coil, a circuit including a coil controlled by said contactor and a contactor operated by said lastnamed coil.

ALBERT R. STARGARDTER.- 

